Suggest Remedy For Painful Bump On Penis

My boyfriend has been getting a single or coupkle pimple like bump after we have sex on his thighs where my fluids drip and once on his penis . thjis has not always been the case but in the past few months it has happened and its not an std because ive tested and im clear. they are slighly painful to the touch and look a bit like a smal pimple without the white part